What is the origin of the word blackmail?

Answer 1

Its origin had nothing to do with the post office. Mail in this sense was an old Anglo-Norse term for rent or tribute. During the time of border warfare between England and Scotland, freebooters extorted payment from farmers of the area in exchange for protection and immunity from plunder. As the inhabitants were generally very poor, the tribute was paid in "black mail," that is, grain, meat, or the lowest coinage (copper), as opposed to "white mail," which was silver. In time the word took on the meaning of any payment extorted by threat of exposure of an incriminating secret.